1. Field of the Invention
The present invention relates to the vehicle-mounted receiving apparatus suitable for receiving while moving, such as a vehicle-mounted television or a portable television.
2. Description of the Related Art
A vehicle-mounted diversity receiving apparatus according to the related art will be described with reference to FIG. 9. High frequency signals, of an OFDM (orthogonal frequency division multiplexing) system, having the same frequencies that are received through receiving antennas 1 and 5 are amplified by high frequency receivers 2 and 6 and are then input to mixers 3 and 7, respectively. Local oscillation signals, of which frequencies are different from each other but adjacent to each other, are applied to the mixers 3 and 7 from local oscillators 4 and 8. For this reason, the mixers 3 and 7 output intermediate frequency signals of which frequencies are different from each other but adjacent to each other. The intermediate frequency signals output from the respective mixers 3 and 7 are synthesized by a synthesizer 9. After the synthesized signals are output from the synthesizer 9, the clock to be used in the receiving apparatus is regenerated by a synchronization circuit 10, and digital signals are obtained by an A/D converter 11.
The digital signals are converted into signals corresponding to carrier waves of the respective frequencies that form the OFDM signals by means of an FFT 12, and are then diversity-synthesized by a synthesizing circuit 13. Then, the digital signals are demodulated by a carrier wave demodulating circuit 14 for each carrier wave. In addition, after an error correction is performed by an error correcting circuit 15, the digital signals are output as digital output data (for example, see JP-A-2000-041020 (FIG. 1)).
When the above-described diversity receiving apparatus is mounted on a vehicle so as to receive television signals and signals such as GPS signals, each of the antennas is mounted on a front glass of the vehicle, and the antennas are connected to a main body of a receiver inside the vehicle through cables.
When a receiving apparatus mounted on a moving body receives television signals, the range of a change in the electric field intensity caused by movement is so large that the electric field intensity may change within a range of +10 dBm to −90 dBm, for example. For this reason, when OFDM-modulated signals, such as terrestrial digital television signals, having a number of carriers, are received in a strong electric field region, the distortion occurs in an amplifier provided in a high frequency receiver. Accordingly, a carrier-to-noise ratio (C/N) is deteriorated, so that a receiving error occurs.